Motorcycle engines commonly have a built-in transmission, so that the crankcase also serves as the case for the transmission. Increase of the displacement of known engines of this type is accompanied by an increase in its length and width. The disadvantage inherent in enlargement of these dimensions is that when a motorcycle is turned, its body inclines laterally. Therefore, if the width of the engine (relative to the direction of forward travel) is increased, the attainable angle of bank, i.e., the angle by which the body can be inclined is decreased. With this in mind, it is a valid objective that the engine width should be made as small as possible, and that the attainable angles of bank at both sides of the vehicle are substantially identical.
The foregoing objectives are met with an engine according to this invention in which an intermediate shaft is interposed between a crankshaft and a transmission. In prior art engines, where there is no provision of the intermediate shaft, the rotations of the crankshaft have to be transmitted directly to the transmission main shaft. Since this main shaft is equipped at its center portion with a transmission gear train, the rotations of the crankshaft have to be transmitted to one end of the main shaft so that the transmission bulges sideways of the engine, with a resultant increase in the engine width. By effecting power transmission through the intermediate shaft, the transmission can be laid out in alignment with the center line of the engine, without requiring the transmission to bulge sideways of the engine.
Also in a conventional engine, the main and counter shafts of the transmission and the crankshaft are rotatably supported in the joint plane of the case. The length of the engine in the direction perpendicular to the crankshaft is accordingly increased. As a result, the motorcycle having a very restricted space available for mounting the engine is accompanied by the drawback that the mounting of the engine itself becomes difficult, and that the wheel base has to be increased.
The present invention provides a vehicular engine which can reduce the length in the direction perpendicular to the crankshaft. In order to attain this objective, the vehicular engine according to the present invention is so constructed that the crankshaft case is disposed above its joint plane with the transmission case, whereas the intermediate shaft is disposed below the same joint plane.